Koi Pond Yoyo

Design for Manufacturing / Spring 2020

Skills: CAD (Fusion 360), CAM, CNC Machining, Thermoforming, Injection molding simulation (Moldflow)

This project was inspired by the aesthetics of fish in a koi pond. Our yoyo was designed to balance manufacturability at scale, easy of assembly, and aesthetic appeal. Our yoyo was composed of 6 injection molded parts, 2 thermoformed parts, and 4 3D-printed parts. More documentation on the design process, manufacturability analysis, and proposed factory layout to produce 1 million yoyos as scale can be found on our team website.

This project was created in collaboration with 3 other mechanical engineering students. I was personally responsible for designof the koi, and running & analyzing all moldflow simulations.

Due to the COVID-19 pandemic, MIT students were sent home in March 2020, so we did not have the opportunity to manufacture our yoyos. Instead, we pivoted to spend increased time running and analyzing simulations of the injection molding process and manufacturing-at-scale.

Process:

Version 1:

Our original design contained several small, detailed features that we were unsure about the feasibility of machining. In particular, we were concerned about how best to manufacture the koi fish and the lily-pad border. We initially planned to overmold the koi fish. to achieve the speckled red and white coloration that we desired. In addition, we planned to press fit each lily-pad nub onto the border. The first iteration contained 9 separate pieces per half-yoyo, with multiple press fits. After receiving feedback, we realized that many of those press-fits could be simplified to loose fits, eliminating some critical dimensions.

Final Version:

The final yoyo design contains 6 pieces that fit together with just 1 snap fit, making the design much more suitable for manufacturing at-scale. We made several critical changes. We pivoted to 3D printing with screen-printing to create the koi fish, allowing us to maintain the small dimensions that we desired. In addition, we decided to overmold the lily pads, and iterated on their design several times. This allows for a more efficient assembly process, where each lil-pad does not have to be press fit into place.

We used Autodesk Moldflow to simulate the injection molding process and find the optimal injection molding conditions. We then used Fusion 360 to make the CAD and CAM for the tooling. We used Siemens Technomatix to create a factory layout that could create 1 million yoyos per year.

V1 & V2: Our initial multiple gates and one gate design; neither were suitable for our equipment

V3: The runner was moved from the side of the part to the center, reducing short shot. Dimensional changes to the thickness of the part were also made, to further reduce short-shot.

Course Description:

2.008 introduces students to modern manufacturing with four areas of emphasis: manufacturing processes, equipment/control, systems, and design for manufacturing. The course exposes students to integration of engineering and management disciplines for determining manufacturing rate, cost, quality and flexibility. Topics include process physics, equipment design and automation/control, quality, design for manufacturing, industrial management, and systems design and operation.